Mechanics of Advanced Composite StructuresMechanics of Advanced Composite Structures
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Feed provided by Mechanics of Advanced Composite Structures. Click to visit.Cured Poly(ethylene-g-maleic anhydride)/Graphene Nanocomposite: Properties and Characterization
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Poly(ethylene-g-maleic anhydride) (PEMA)/graphene nanoplatelets (xGn) (PEMA-xGn) composites were prepared by melt dispersion in an internal shear mixer. By adding dicumyl peroxide (DCP), cured poly(ethylene-g-maleic anhydride) C-PEMA was also produced. Different amounts of xGn were introduced into the PEMA in range of 0.5–5 wt. %. The effects of the sequence of feeding additives into the mixer on gel content, morphology, and mechanical properties allowed thermal, dynamic mechanical, and rheological behaviors to be studied. Results demonstrated that the incorporation of graphene into the polymer matrix decreased gel content and the rate of crosslinking. Scanning electron microscopy micrographs of the PEMA and C-PEMA nanocomposites showed that below 1 wt. % graphene, its dispersion in the matrix was desirable with no agglomerates.. Crystallization temperature increased due to heterogeneous nucleation by xGn. By curing the nanocomposites with DCP, crystallization temperatures decrease due to crosslinking and decreased crystallinity. The results of crosslinked nanocomposites revealed that, with the exception of C-PEMA containing 0.5 wt. % of xGn, mechanical properties decreased as xGn concentrations increased. Dynamic mechanical analysis showed that the increase of xGn in the PEMA matrix of up to 1 wt. % led to increased storage and loss modulus values. It was also revealed that α-transitions of the PEMA and α- and γ-transitions of C-PEMA were affected by polymer chain branching and graphene nanoplatelets. This could be attributed to interactions and potential bond formations between xGn and the maleic anhydride of PEMA. Rheological properties of the PEMA nanocomposites showed a quick change in the xGn fraction at about 1 wt. %.Sat, 31 Mar 2018 19:30:00 +0100Experimental investigation on the strength of concrete containing glass fiber subjected to high ...
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The present study aims to investigate the effect of increased duration of high temperature on compressive, tensile, and flexural strength of concrete containing glass fiber at a rate of 1%, 2%, and 3% exposed to high temperature (600 °C) in three different target times including 30 minutes, one hour, and two hours. Samples were cooled in two ways: slow cooling (exposure to air) and fast cooling (water spray immediately after exposure to heat). A total of 84 cubic samples (size: 150×150×150 mm), cylindrical samples (size: 300×150 mm), and prismatic samples (size: 500×150×150 mm) were prepared for studying compressive strength, tensile strength, and flexural strength, respectively. After 28 days of processing and gaining the re-quired strength, samples were put in annealing furnace and the experiments were conducted. The results showed that the presence of glass fiber has a considerable impact on concrete of exposed to high temperature. Also, heat causes many cracks in concrete samples.Sat, 22 Sep 2018 20:30:00 +0100Bending, buckling and free vibration responses of hyperbolic shear deformable FGM beams
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This study investigated bending, buckling, and free vibration responses of hyperbolic shear deformable functionally graded (FG) higher order beams. The material properties of FG beams are varied through thickness according to power law distribution; here, the FG beam was made of aluminium/alumina, and the hyperbolic shear deformation theory was used to evaluate the effect of shear deformation in the beam. The theory explains the hyperbolic cosine distribution of transverse shear stress through the thickness of a beam and satisfies zero traction boundary conditions on the top and bottom surfaces without requiring a shear correction factor. Hamilton’s principle was employed to derive the equations of motion, and analytical solutions for simply supported boundary conditions were obtained using Navier’s solution technique. The non-dimensional displacements, stress, natural frequencies, and critical buckling loads of FG beams were obtained for various values of the power law exponent. The numerical results were compared to previously published results and found to be in excellent agreement with these.Sat, 31 Mar 2018 19:30:00 +0100Optimization of infinite composite plates with quasi-triangular hole under in-plane loading
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In this study an attempt has been made to introduce the optimal value of effective parameters on the stress distribution around a quasi-triangular hole in an infinite orthotropic plate using particle swarm optimization algorithm (PSO). The present study is based on the development of an analytical method conducted by Lekhnitskii for infinite anisotropic plate with a circular or elliptical hole. In this study, load angle, hole orientation, bluntness, fiber angle and material properties are design variables. Cost function is the maximum stress created around the hole calculated by the analytical solution method. Also, the performance of the optimization algorithm is investigated. Finite element numerical solution is employed to examine the results of present analytical solution. Overlap of the results of the two methods confirms the validity of the presented solution. The results showed that these parameters have significant effects on stress distribution around the holes and the structural load-bearing capacity.Sat, 22 Sep 2018 20:30:00 +0100Sensitivity Analysis of Fiber-Reinforced Lamina Micro-Electro-Mechanical Switches with ...
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In this paper, the nonlinear free vibration of fiber-reinforced lamina micro-switches is investigated, and a sensitivity analysis (SA) is given. The switches are modeled as solid rectangular beams consisting of an isotropic matrix with transversely and longitudinally isotropic reinforcements, incorporating a higher order Hamiltonian approach. An SA of the proposed micro-switch is presented by calculating the numerical derivatives of the presented nonlinear model with respect to the design parameters. The SA of geometric parameters, such as dimensionless length, thickness, initial gap, applied voltage, axial load, and effective modules of the system, was conducted using the Sobol method. It was found that the natural frequency varied when changes were made to the proposed parameters; this finding can be used to optimize future designs.Sat, 31 Mar 2018 19:30:00 +0100Distribution effect of Fe3O4 nanoparticles on the mechanical properties of Al-Fe3O4 ...
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In this study, a new nano-structured Al / Fe3O4 composites produced by the ARB process has been introduced. XRD analysis test and FESEM microscopic images were used to examine microstructure characteristics of the nanocomposite. The microstructure and distribution of the particles in the composite were investigated by the X-ray diffraction methods and field emission scanning electron microscopy (FESEM) micrograph. The Al crystal size Al reached to 198 nm after 8 cycles by XRD analysis. The hardness and tensile strength tests were employed for the mechanical properties. Finally, the mechanical properties of the composite, i.e. tensile strength and hardness, achieved to 204 MPa and 63 HV after 8 cycles, respectively that are a high value compared to pure aluminum. In addition, the levels of the nanocomposite rupture revealed that a ductile fracture occurred by formation and growth of cavities. 4. Surface fracture shows mechanism fracture is the ductile rupture and by increasing the number of ARB cycles, particles disperse uniform and the number of shallow voids increase.Sat, 22 Sep 2018 20:30:00 +0100Experimental Study on Amine-Functionalized Carbon Nanotubes’ Effect on the Thermomechanical ...
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This paper investigated the effect of the amine-functionalized carbon nanotubes (CNTs) on the thermomechanical properties of CNT/epoxy nanocomposites. Mechanical stirring and ultra-sonication were utilized to uniformly disperse CNTs into the epoxy matrix. Non-functionalized and amine-functionalized CNTs with different weight percentages (wt. %) were mixed into the epoxy resin. Using standard tensile and dilatometry test specimens, this paper determined Young’s modulus, ultimate strength, strain at break, coefficients of thermal expansion, glass transition temperature (Tg), and thermal strain at Tg of the specimens. Neat epoxy, non-functionalized CNT/epoxy (0.25 and 0.5 wt. % CNTs), and functionalized CNT/epoxy (0.25 and 0.5 wt. % functionalized CNTs) nanocomposites were studied. The results indicated that adding 0.25 wt. % functionalized CNTs into the epoxy resin had the greatest effect on Young’s modulus and the nanocomposites’ coefficient of thermal expansion. Moreover, adding CNTs into the epoxy resin decreased the ultimate strength, strain at break, and coefficient of thermal expansion of the specimens.Sat, 31 Mar 2018 19:30:00 +0100An Analytical approach for Thermoelastic Bending of Simply-Supported Ribbed Advanced Composite ...
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In present paper thermal deflections of a simply supported composite plate in pres-ence of a beam-like stiffener is studied by making use of an analytical approach. The results will be presented for the plate-beam system exposed to sinusoidal thermal load in order to study the effects Low Earth Orbit (LEO) thermal conditions on the composite plates which has been used in the structure of satellites and spacecrafts. The thermal boundary condition on one side of the plate has been considered to be in a sinusoidal form which is common in LEO satellite applications. The temperature equation with the assumption of small rate of strains has been un-coupled from the equation of motion of plate by omitting the coupling term of displacement from temperature equation and the quasi-static equation of heat conduction has been solved separately by making use of Laplace transform method. In order to solve the governing equations of the system the Laplace trans-form method (for the time domain) in conjunction with Navier Series expansions has been used. Since the employed method is completely analytical the results are exact.Sat, 22 Sep 2018 20:30:00 +0100Three-dimensional elasticity solution for vibrational analysis of thick continuously graded ...
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An equivalent continuum model based on the Eshelby-Mori-Tanaka approach was employed to estimate the effective constitutive law for an elastic isotropic medium (i.e., the matrix) with oriented straight carbon nanotubes (CNTs). The two-dimensional generalized differential quadrature method was an efficient and accurate numerical tool for discretizing equations of motion and for implementing various boundary conditions. The proposed rectangular plates have two opposite edges simply supported, and all possible combinations of free, simply supported, and clamped boundary conditions were applied to the other two edges. The CNTs volume fraction varied based on the thickness of the functionally graded carbon nanotube-reinforced plate and the generalized power-law distribution of four parameters. The effects of geometrical and material parameters and boundary conditions on the frequency parameters of the laminated functionally graded nanocomposite plates were investigated, and the results revealed that the natural frequencies of the structure were significantly affected by the influence of CNT agglomeration.Sat, 31 Mar 2018 19:30:00 +0100Creep strain and stress analysis in laminated composite pressure vessels
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Time-dependent long term creep strain in composite cylinder made of glass/vinylester with unidirectional ply is investigated in this study. The cylinder is subjected to an internal pressure, boundary condition is free-free and it acts as a thermal insulation. Classical lamination theory (CLT) is used to derive governing equtions as a second-order equation for radial displacement based on plane strain model. By solving second-order equation, radial, circumferential, axial and effective stresses in the cylinder wall is calculated. Distribution of radial and circumferential creep strains based on Schapery single integral model for nonlinear viscoelastic materials demonstrated. The detailed parametric study is conducted, focusing on the effect of fiber orientations on the way of creep distribution in in the wall of cylinder .The results show that in fibers angle θ=45° creep strains lower than fiber angle θ=90°. The results show that the more the fibers angle increases, the more uniform the distribution of creep strain becomes.Sat, 22 Sep 2018 20:30:00 +0100Theoretical, numerical, and experimental analyses of free vibrations of glass fiber reinforced ...
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This study explored the free vibration problem in relation to glass fiber reinforced polymer (GFRP) plates with central cutouts and free boundaries using theoretical, experimental, and numerical methods. The theoretical formulations were derived from the classical lamination plate theory. The rectangular cutout was mathematically modeled into the stiffness matrix of the plate by multiplying Heaviside distribution functions. The theoretical values for the fundamental frequency were obtained by solving the standard eigenvalue problem, and the theoretical solution was validated by comparison to the literature. Modal testing was performed in the laboratory. For additional validation, the accuracy of theoretical and experimental results was checked using the finite element method and ABAQUS. The results of all three methods agreed; thus, the applicability of the Heaviside functions to stiffness modeling of structures with cutouts was proven. It was also observed that the fundamental frequency decreased when cutout size increased.Sat, 31 Mar 2018 19:30:00 +0100Flexural Behavior of Surface Functionalized Nanoclay Reinforced Fiber-Metal Laminates
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The effect of adding surface functionalized Na+-montmorillonite (MMT) nanoclay at various weight percentages of 1, 3, 5 and 7 with respect to the matrix on the mechanical behavior of glass reinforced aluminum (GLARE) laminates in transverse loading was investigated. The nanoclay particles were surface functionalized with 3-(Trimethoxysilyl)propylamine (3-TMSPA) to increase their compatibility with the epoxy matrix and improve their dispersion within the matrix. Experimental results indicated that the highest values in flexural strength and energy absorption were achieved in the GLARE laminate at 3 wt.% functionalized nanoclay addition, i.e., 61% and 51% increases, respectively. However, the highest flexural modulus (67% increase) was observed at 5 wt.% functionalized nanoclay. Moreover, the flexural properties of the functionalized nanoclay filled GLARE laminates were significantly greater than those of the untreated nanoclay filled laminates. Microscopic observations suggested that the introduction of functionalized nanoclay particles markedly enhanced the interfacial adhesion between the matrix and the E-glass fibers.Sat, 22 Sep 2018 20:30:00 +0100Evaluation of hardness and wear resistance of nano-sized titanium-carbide-reinforced ...
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Production of aluminum matrix composites is widespread because these material provide enhanced mechanical properties compared to aluminum. One the most important parameters of metal matrix composite production is uniform distribution of reinforcing nanoparticles in matrices using the stir-casting method. Second is ensuring high wettability, which is determined by evaluating the properties of materials on a nano-scale. In this study, aluminum composites were reinforced with titanium carbide nanoparticles coated with aluminum to increase wettability. Particles were prepared and added to a molten aluminum alloy. After stirring the particle mixture as a variable parameter, casting was conducted in a sand mold. To evaluate the mechanical properties of the composite, the Brinell test was used to determine hardness and the pin-on-disk test was used to measure wear rate and the friction coefficient. The results showed that the hardness of the composite increased from 84 BHN to 134 BHN as nanoparticles were added to the alloy. Additionally, as stirring time increased, weight loss decreased with respect to the base alloy, while the coefficient of friction increased.Sat, 31 Mar 2018 19:30:00 +0100Improving the Performance of Porous Concrete Composite with Zeolite as Coarse Grain
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Porous concrete is a mixture of cement and water, with/without some fine grains, which is im-portant in terms of water transfer and permeability. This type of concrete can act as a drain, pass rainwater and recharge groundwater. In this experimental study, effect of replacing zeolite (25, 50, 75 and 100 percent) for coarse aggregates in porous concrete on its compressive strength, permeability coefficient, porosity and density was investigated. Results showed that with the replacement of zeolite in the structure of porous concrete and corresponding removal of aggregates, compressive strength of the samples was reduced, due to the porous nature of zeolite, and the most important parameters affecting the performance of porous concrete such as permeability coefficient and porosity, were increased. The highest compressive strength (10.29 MPa) was observed in the specimen containing 25% zeolite and the lowest compressive strength (6.79 MPa) was observed in the specimen containing 100% zeolite. The highest porosi-ty (30.97%) and permeability coefficient (1.76 mm/s) was measured in the 100% zeolite sample. Permeability coefficient was increased by 6.99, 17.39, 21.3 and 24.4 percent, respectively, and density was reduced by 7.77, 10, 15, and 19.44 percent, respectively, with respect to the control, in the aforementioned four zeolite treatments.Sat, 22 Sep 2018 20:30:00 +0100Capillary Effects on Surface Enhancement in a Non-Homogeneous Fibrous Porous Medium
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The evaluation of a free fluid surface in a porous medium has several mathematical applications that are important in industries using molds, particularly in the fluid injection process. The vacuum-assisted resin transfer molding (VARTM) process is a promising technology in the primary composite industry. An accurate computational simulation of the VARTM process would be a cost-effective tool in the manufacturing of composites. In this paper, capillary effects were incorporated into an existing resin transfer molding model to simulate VARTM processing. To increase the accuracy of the VARTM process simulation, the effect of capillary pressure on a surface without flow was studied using the boundary element method. The simulation results were close to the experimental data reported by other researchers. It can be concluded that better reliability and accuracy could be achieved from theoretical predictions by examining the effects of capillary pressure on flow injection into porous materials.Sat, 31 Mar 2018 19:30:00 +0100Elasto-thermodiffusive Response in a Two Dimensional Transversely Isotropic Medium
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The present article deals with the investigation of elasto-thermodiffusive interactions in a transversely isotropic elastic medium in the context of thermoelasticity with one relaxation time and two relaxation time parameters respecytively. The resulting non-dimensional coupled equations are applied to a specific problem of a half-space in which the surface is free of tractions and is subjected to time-dependent thermal loading and chemical loadings. The analytical expressions for the displacement components, stresses, temperature, strain, mass diffusion and the chemical potential are obtained in the physical domain by employing the normal mode analysis as a tool. These expressions are also calculated for a copper-like material and have been depicted graphically. A comparative study of diffusive medium and thermoelastic medium is carried out and it was seen that the effect of diffusion is significant on the thermophysical quantities. Further, it is also observed that in absence of the effect of thermodiffusion, the results agree with the results of existing literature.Sat, 22 Sep 2018 20:30:00 +0100Geometric Effects on Nanopore Creation in Graphene and on the Impact-withstanding Efficiency of ...
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Abstract Single- and multilayer graphene sheets (MLGSs) are projectile-resisting materials that can be bombarded by nanoparticles to produce graphene sheets of various sizes and distributions of nanopores. These sheets are used in a variety of applications, including DNA sequencing, water desalination, and phase separation. Here, the impact-withstanding efficiency of graphene nanosheets and the primary factors affecting creation of nanopores in these sheets were studied using a molecular dynamics method. The velocity of impacting nanoparticles and resulting displacement in graphene nanosheets are not sufficient criteria for evaluating the impact resistance of sheets with more than six layers. Instead, visual inspection of the bottom side of a graphene sheet should be used. Self-healing is the most important aspect of MLGSs because it closes the paths of penetrating nanoparticles in the upper layers of the sheets. For nanosheets with few layers, self-healing is observed only at very small nanoparticle velocities; however, when the number of layers is more than six, self-healing occurs even at high nanoparticle velocities. In nanoribbon simulations, it was found that layer boundaries improve resistance against projectile impacts that create well-defined oval shapes. By increasing the distance between layers, the carbon atoms of each layer experience more collisions with the carbon atoms of other layers. Thus, increasing the interlayer distance causes the number of unwanted collisions between carbon atoms to increase and the graphene nanosheets to disintegrate. Additionally, as the circularity of nanopores increases, they become more circular and homogeneous, in turn increasing interlayer spacing, the impact-withstanding efficiency of the sheets, and the circular shape of created nanopores.Sat, 31 Mar 2018 19:30:00 +0100Thermoelastic interaction in a three dimensional layered sand-wich structure
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To accommodate the mirco-structural effects, the present article deals with the thermoelastic interaction in a three-dimensional homogeneous and isotropic plate of sandwich structure under the framework of Dual-phase-lag (DPL) model of generalized thermoelasticity. The incorporated resulting non-dimensional coupled equations are applied to a specific problem of a sandwich layer of unidentical substances, each of which is homogeneous and isotropic, whose two outer sides are traction-free and is subjected to time-dependent thermal loadings. The analytical expressions for the displacement components, stress, temperature and strain are obtained in the physical domain by employing normal mode analysis. A numerical scheme has been developed to overcome the mathematical difficulties in dealing with the hyperbolic heat conduction equation and the thermophyscial quantities have been depicted graphically for the sandwich structure. Discussions have been made to highlight the effect two phase lags on the studied field. The results demonstrates the phenomenon of a finite speed of wave propagation in the sandwich structure for each field Also.Sat, 22 Sep 2018 20:30:00 +0100Investigation of Capsulated Epoxy and DCPD in Epoxy Based Self-healing Composites - DFT ...
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Epoxy and dicyclopentadien (DCPD) are two common healing agents which are introduced to epoxy matrix through encapsulation in order to prepare self-healing composites. In a compara-tive study the compatibility of healing agents and epoxy matrix were investigated through ex-perimental and DFT calculations. The interaction energy was considered to be the determination parameter in DFT calculation. The values of total interaction energy were -0.14eV for DCPD and +0.169eV for epoxy absorbing on epoxy matrix. DFT results showed an attraction between DCPD and epoxy matrix. DOS and charge analysis of these systems was fulfilled which demonstrated the charge transfer of 0.07 e from epoxy to DCPD. The obtained data revealed the most charge transfer in DCPD-epoxy which would affect the mechanical properties of healed composites. To examine the mechanical properties, tensile strength parameters were measured and the experimental results demonstrated improved ultimate strength of 783.49 MPa in DCPD/epoxy system rather than the resulted ultimate strength of 571.87 MPa in epoxy/epoxy system. Also elongation at break in DCPD-epoxy system was improved to 3.44% while it was 1.84% in epoxy/ epoxy blend. These findings highlight the role of interaction energy in mechanical properties of polymeric interface, and prompt further experiments and simulations to confirm this effect.Sat, 22 Sep 2018 20:30:00 +0100